How to select meshes with transparent materials applied to them only?
Generally determining if a given node setup is transparent is rather tricky; for instance, a material may be transparent only in some areas (textured transparency) and other such complications. However, in your case, it seems that checking if the value of the "Mix Color/Alpha" node is &lt; 1 should be sufficient.

for obj in bpy.data.objects:
    if obj.type == 'MESH':
        for slot in obj.material_slots:
            if slot.material:
                mat = slot.material
                for node in mat.node_tree.nodes:
                    if node.label == "Mix Color/Alpha":
                        if node.inputs[1].default_value[0] &lt; 1:
                            print("Material '%s' on object '%s' seems transparent" % (mat.name, obj.name))


The importer seems to create both cycles and BI materials, so you could also check the BI material property (even while cycles is active):

for obj in bpy.data.objects:
    if obj.type == 'MESH':
        for slot in obj.material_slots:
            if slot.material:
                mat = slot.material
                if mat.use_transparency:
                    print("Material '%s' on object '%s' seems transparent" % (mat.name, obj.name))